Use derive_default_enum in the compiler

compiler/rustc_trait_selection/src/lib.rs

@@ -14,6 +14,7 @@
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
 #![feature(drain_filter)]
+#![feature(derive_default_enum)]
 #![feature(hash_drain_filter)]
 #![feature(in_band_lifetimes)]
 #![feature(iter_zip)]

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -82,9 +82,14 @@ pub use self::chalk_fulfill::FulfillmentContext as ChalkFulfillmentContext;
 pub use rustc_infer::traits::*;
 
 /// Whether to skip the leak check, as part of a future compatibility warning step.
-#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+///
+/// The "default" for skip-leak-check corresponds to the current
+/// behavior (do not skip the leak check) -- not the behavior we are
+/// transitioning into.
+#[derive(Copy, Clone, PartialEq, Eq, Debug, Default)]
 pub enum SkipLeakCheck {
     Yes,
+    #[default]
     No,
 }
 
@@ -94,15 +99,6 @@ impl SkipLeakCheck {
     }
 }
 
-/// The "default" for skip-leak-check corresponds to the current
-/// behavior (do not skip the leak check) -- not the behavior we are
-/// transitioning into.
-impl Default for SkipLeakCheck {
-    fn default() -> Self {
-        SkipLeakCheck::No
-    }
-}
-
 /// The mode that trait queries run in.
 #[derive(Copy, Clone, PartialEq, Eq, Debug)]
 pub enum TraitQueryMode {